Internal Combustion Engine Fundamentals

  • Thread starter sid_galt
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  • #1
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In an SI engine, according to the book Internal Combustion Engine Fundamentals, knocking is produced due to the interaction of the shock wave and the expansion wave which together produce very high amplitude standing waves.

My question is, in knocking is there only one shock wave or multiple shock waves?

Would a single shock wave with a low pressure gradient (say 1 bar) be sufficient to damage the engine?
 

Answers and Replies

  • #2
Clausius2
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sid_galt said:
In an SI engine, according to the book Internal Combustion Engine Fundamentals, knocking is produced due to the interaction of the shock wave and the expansion wave which together produce very high amplitude standing waves.
My question is, in knocking is there only one shock wave or multiple shock waves?
Would a single shock wave with a low pressure gradient (say 1 bar) be sufficient to damage the engine?

I have never heard that knocking was caused by that. That's a poor explanation of knocking, which has its ultimate fundamentals in the Chemics involved.

You shouldn't view knocking as a single detonative shock wave travelling inside the cylinder. Knocking is caused locally, in each element of mixture, and spreads a great amount of small spheroidal shocks which interact one each other. All of them gather togheter to form a pressure front.

On the other hand, I doubt very much that a shock wave with such a low pressure gradient can exist. You should be able to work out how much damage can provoke. Just solve the pressure produced and calculate the stress exerted by the explosion in the piston rod, and compare it with the elastic limit of steel.
 
  • #3
Danger
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Speaking as one who has blown a hole the size of a golf ball in a piston... ouch!
 

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